In general, it is common in the field that video switching jacks are used to sense when signal leads are plugged into the jacks. A line couples the status of the jack to a pin of the video switching integrated circuit (IC) and a corresponding status bit is set. A programmable microprocessor reads the status over the bus, e.g., an I2C bus, and configures electronic switches of the video switching IC according to an algorithm.
The present device, is a television set/receiver with or without a video display. In a typical receiver, all input signals are coupled to an audio/video switch IC. The desired input is normally selected from a menu using an input key on a remote control. The menu will sequentially cycle through the input states in a wrap-around endless loop.
More particularly, the present invention concerns a CXA2089 switch IC made by the Sony Corp. of Japan. For each input state, a designated pin on the switch IC is used to detect a signal presence, and in response thereto, a corresponding bit is stored in a designated register(s). The microprocessor reads the register(s) over the bus and reacts according to a preprogrammed algorithm to close or open the proper switches of the IC. The CXA2089, has only three such input terminals to sense signal presence, and in the present situation, not only were all of these input terminals used, but even more were required for sensing additional input signal requirements, as discussed more fully below.
It should be noted that the television receiver often has both front and rear panel jacks for accepting plugs with various signals. The rear or non-front panel signals provide a basic set-up for the device with the basic set-up being changeable by the presence of front panel signals, since the front panel signals are user changes of more immediate status. In the particular case, it is further desirable to have a front panel composite video override any of the other states or conditions, and then to have an S-video component signal, if plugged into a front jack, to override the front composite video as well as the other states. However, these extra switching requirements require two extra input sense pins on the switch IC, and, as stated above, all of the conventional pins were being used for other switching requirements and thus, were not available.
However, the switch IC has three of what are called “S2 protocol” input switching pins (discussed more fully below), which are designed to be used to select picture aspect ratio by sensing DC voltage on the chroma signal. Aspect ratio is not an issue for this receiver because all signals have a 4:3 aspect ratio. However, by applying the proper DC voltages to one or more of these S2 protocol pins, further bits can be stored in corresponding registers in the switch IC, the microprocessor can then read these bits over the bus, and close the proper switch IC switches according to a preprogrammed algorithm to have the front composite signal override all other input signals and to have front S-Video component signal override the front composite signal as well as all other input signals.
When S-video component signals were first originated, it was decided that a DC signal could be applied to the chrominance signal to indicate to a receiving device that a change of aspect ratio was to be initiated. A change of aspect ratio indicated by the introduction of a DC bias voltage to the chroma signal for a 16:9 anamorphic picture is shown in Lagoni, U.S. Pat. No. 5,629,776, assigned to an antecessor of the assignee of the present patent application. Over the years, the S-video aspect ratio indicator signal has been expanded to include three levels, i.e., tri-state, of input DC voltage plus zero, and is called the “S2 protocol” according to EIAJ standard No. CPR-1202, for “Identification Signal of Video Signals With Different Aspect Ratio and the Transfer Methods”. Thus, it is desirable to use these S2 protocol compliant pins for an unintended purpose, i.e., to trick the S2 protocol input terminals into initiating the switching of non-S2 protocol signals. Additionally, such S2 protocol integrated circuit input terminals are designed to be responsive to the DC level of a single type of input signal coupled to the particular pin, i.e., each pin is to receive its own single signal corresponding to the S2 protocol on an individual basis.